Elastomeric block copolymers having vinylarene polymer blocks and olefinic and/or diene polymer blocks typically exhibit a bi-phasic morphology, in which similar blocks come together to form one phase distinct from a second phase formed by the other blocks. The block copolymers form a three-dimensional, entangled (i.e., physical crosslinks) network structure. The polymeric chains may move about and disentangle from those physical crosslinks, resulting in loss of elastic and mechanical properties. Low molecular weight crosslinking agents have been used to create chemical crosslinks among polymeric chains to improve properties. However, it is known that small molecules are thermodynamically more compatible, thus, less selective, with respect to both phases of the bi-phasic copolymers. Consequently, low molecular weight crosslinking agents are intimately mixed with both phases of the copolymers and crosslinks indiscriminately in both phases. The resulting materials may become more difficult to process and more brittle in use. Approaches to selectively crosslink one phase are also known. Elastomeric compositions containing general and selective crosslinking agents are disclosed in U.S. Pat. No. 4,133,731 (Hansen et al.); U.S. Pat. No. 4,556,464 (St. Claire); U.S. Pat. No. 5,073,611 (Rehmer et al.); U.S. Pat. No. 5,407,971 (Everaerts et al.); U.S. Pat. No. 6,294,698 (Nohr et al.); U.S. Pat. No. 6,369,123 (Stark et al.); and U.S. Pat. No. 6,384,139 (Ho et al.).
There is a continuing need for curable elastomeric compositions that are selectively crosslinked to provide improved elastic and mechanical properties and still maintain the processability of thermoplastics.
Elasticized portions of health care or personal hygiene products are conformable to the body, and create a relatively occlusive environment under the products. As materials with greater elasticity are used in such products to provide a better fit to the body, the air flow to the skin and the vapor flow from the occluded areas are reduced. Breathability (particularly vapor permeability) becomes an important factor for skin health. Several methods for rendering elastomeric materials more porous and more breathable are known in the art, such as die punching, slitting, and hot-pin aperturing. Improved methods to produce better porous films or webs, such as macroscopically-expanded, three-dimensional webs, are disclosed in U.S. Pat. No. 3,929,135 (Thompson); U.S. Pat. No. 4,342,314 (Radel et al.); U.S. Pat. No. 5,733,628 (Pelkie); U.S. Pat. No. 6,303,208 (Pelkie); and PCT Publication WO 98/37266 (Curro et al.).
There is considerable difficulty in processing and handling elastomeric materials, due to the inherent tacky and stretchy nature of the elastomeric materials. The elastomeric materials have a tendency, to stick to the processing equipment, and are difficult to remove from a roll or cut to the correct size to be incorporated into the finished products. Further, the elastomeric materials may be joined to non-elastomeric substrates, such as inelastic nonwoven materials, and means to impart elasticity to the resulting laminates are desirable. Various processes for imparting elasticity are disclosed in U.S. Pat. No. 4,153,664 (Sabee); U.S. Pat. No. 5,143,679 (Weber et al.); U.S. Pat. No. 5,156,793 (Buell et al.); U.S. Pat. No. 5,167,897 (Weber et al.); U.S. Pat. No. 5,518,801 (Chappell et al.); U.S. Pat. No. 5,628,097 (Benson et al.); U.S. Pat. No. 5,650,214 (Anderson et al.). However, various elastomeric materials are known to suffer defects, such as pinholes, fisheyes, or the like, under the above processes or combinations thereof. Such defects in the elastomeric materials may act as stress concentrators that promote tear initiation, tear propagation and catastrophic failure of the materials during use.
Therefore, there is a continuing need for elastomeric materials that provide elasticity (including low stress relaxation) and breathability as well as processability.
It is desirable to have melt processable elastomeric compositions that may be preferentially crosslinked in a select phase of the composition.
It is further desirable to have macromolecular crosslinking agents capable of preferential crosslinking in a select phase of the composition and contributing to improved mechanical and elastic properties of the resulting elastomeric compositions.
It is also desirable to have elastomeric compositions that are suitable for forming elastomeric products, such as apertured or macroscopically-expanded three-dimensional elastomeric webs, or components of absorbent products (including health care products or personal hygiene products) or stretchable garments. The absorbent products may include taped/fastened diapers, pull-on diapers, training pants, incontinence garments, sanitary napkins, pantiliners, wipes, wound dressings, bandages, drapes and wraps.